410 Fisuive is Amertcan WATERS. 
are let up, there is little use in letting the others up. Therefore 
the easier these passages (of whatever kind they may be) are 
made for the salmon, the better it will be for the fishery. 
Now it has been ascertained that a slope of one in seven 
or eight is very near the extreme of steepness which a strong 
salmon can make his way through—that is, for any distance. 
It may be that by a sudden effort of the tail, for a yard or 
two, he can shoot almost any thing, but when he has been a 
dozen yards or more of such gradient, unless he can somehow 
obtain a fresh starting-point, the effort fails, and the fish is 
driven back by the weight of the stream. 
Therefore it is desirable, in all passes which are long or 
full-steep, to have a resting-place, or a quiet pool whence the 
salmon can take wind and make a fresh start. It is impossi- 
ble to lay down any definite rule for the construction of all 
fish-passes, since the architect must be governed by the facil- 
ities or difficulties presented by the dam or fall, and probably 
few dams should be treated precisely the same. Various 
methods have been employed where the water at the pool be- 
low the dam is too shallow to offer the fish a good start to 
leap the obstruction. One of the first and most simple plans 
constructed on the New England and Canadian rivers was a 
series of leaps from pool to pool, with a small dam thrown 
across the stream below in order to raise the water enough 
to give the salmon a start. 
A stone pier is erected above the fall to break the ice in 
spring, and to check the force of the timbers and the heavy 
débris of the stream during spring freshets. 
On small streams, a rough dam of big boulders, logs, ete., 
has been made a few yards below the existing one; this will 
probably be almost half the height of the other, and is com- 
paratively easy to get over. It returns the water against 
the lower face of the original dam, and so makes that much 
easier, and by making a pool between them of some depth, it 
gives the fish the start it requires. This, on small streams, 
has been found very effective, and can not in the least affect 
